Could ISIS use self-driving cars as weapons?
I guess so, but it seems unlikely.
The idea is to achieve the same effects as a suicide bomber, but without the unreliability or cost of a human terrorist.
Firstly, building self-driving cars seems well beyond the technological capability of ISIS.
Secondly, self-driving cars will be far less autonomous then the Model T. They will be connected back to the manufacturer, and presumably subject to government search warrants.
Thirdly, they are expensive.
On a related note, the FBI worries that self-driving cars will be uses for criminal activity generally.
I think the truth might be closer to the opposite. In a world where your car is constantly communicating with the Internet, who would want to use a car for crime?